I have an established 20g tank that is currently home to a male betta, one ADF, and 7 cardinal tetras. These species have gotten along fine for me for years. I once tried adding a mystery snail but the betta abused him horribly, nipping at his antennae anytime they risked leaving the shell. I had to return the poor snail. I'm having more algae than normal lately (which is weird since it's winter and there is less daylight and the lighting of the room/tank haven't changed). It just collects mostly on the glass of the tank and the gravel and decor and I'd love to introduce an algae eater to help keep it under control.

I'm not sure about a pleco unless I could get a small peaceful one. A bristlenose maybe? I clearly can't do a snail. What about otos? I've never had any before. Do they really help keep the algae in check? Would a pleco or oto or other bottom dweller pose a problem for my ADF? The frog isn't always fast to get to its food, but I'd be more worried about a fish latching onto the frog and attempting to eat it!

Have kept Oto's, Bristlenose and Rubberlips with community fish and had no problems . What I like most about them is they do not grow as large as standard pleco's and will max out around 1-1/2 to 2" on the Oto's and 4" on the BNP and RL's. It would take quite a few Oto's to do much damage to algae as they are very small, not really sure how many in a 20 but I would guess around 8 or so, maybe more you need someone else's advice on these. Rubberlips work very hard and clean up a tank quite well, but my fav is the Bristlenose and I would get 1 or 2. Hope this helps you some :)

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Thanks, Byron. I should have described the algae situation more clearly. I don't have any live plants in the tank. Usually I just get a thin brown algae that coats the sides of the tank in patches or the plastic plants and "rock" (what is it really? ceramic? plaster?). It was pretty easily held at bay with an algae scraper during water changes. Sometimes I'd scrub the decor off with a brush too. Lately there is also a dark green algae similar to the brown and in the same places but that also seems to be coating the gravel as well. When I scrape it off it becomes sort of flakey/feathery. My pH is pretty constant at about 6.8. Ammonia and Nitrites at 0. Nitrates usually between 20-40.

The tank is not in direct sunlight and the room it's in is mostly a northern exposure. It's just a 20g basic set up which has some sort of flourescent bulb that is on for maybe 5-7 hours a day. It's a Whisper carbon filter. Not sure what else is pertinent.

Thanks, Byron. I should have described the algae situation more clearly. I don't have any live plants in the tank. Usually I just get a thin brown algae that coats the sides of the tank in patches or the plastic plants and "rock" (what is it really? ceramic? plaster?). It was pretty easily held at bay with an algae scraper during water changes. Sometimes I'd scrub the decor off with a brush too. Lately there is also a dark green algae similar to the brown and in the same places but that also seems to be coating the gravel as well. When I scrape it off it becomes sort of flakey/feathery. My pH is pretty constant at about 6.8. Ammonia and Nitrites at 0. Nitrates usually between 20-40.

The tank is not in direct sunlight and the room it's in is mostly a northern exposure. It's just a 20g basic set up which has some sort of flourescent bulb that is on for maybe 5-7 hours a day. It's a Whisper carbon filter. Not sure what else is pertinent.

Thanks!

This info helps, and clears up things. First, without live plants you have nothing to use the nutrients and light, and algae will be present. This is perfectly natural, and in fact useful. Any of the green or "red" algae function similar to plants in using nutrients (cleaning the water a bit) and producing oxygen. So without plants, these algae are actually useful and beneficial, and can be decorative.

The green you describe is likely a type of brush algae. I see this in a couple tanks, always near the top of some plants, and particularly near the filter outlet/spraybar. The increased water movement is said to encourage it. On plant leaves this is a problem, but otherwise, up to you. Scrape it off as you want.

Now, I've never seen this on the gravel, are you sure this is the same and not cyano? Maybe a photo?

The brown is likely diatoms, which is not a true algae, that will usually occur during the first 2-3 months then no more, but it can persist if light is low and/or there are silicates in the water. This has no aesthetic benefit, at least not to me, and it comes off easily (with your fingers).

There are two fish that will eat the green/red brush algae types, but neither is suited to your 20g. Diatoms will get gobbled up by otos, bristlenose plec, Farlowella vitatta, and perhaps a few others.

Some live plants would help, as these grab nutrients faster and thus use the light so algae is at a disadvantage. Even something as simple as floating plants, which will benefit the fish in more ways than one as well. In fact, your betta and cardinal tetra should never be without floating plants. There are some in our plant profiles.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

The tank has been up and running for almost two years now. Would that mean that the brown algae isn't diatoms? It could be a low light thing. I don't know what silicates are though and why I would have them in my tank.

There are several pictures of this person's tank and in a couple you can see the green feathery algae on the white plants. That looks like what I have. So it's cyano? But this is not a problem right, just unsightly? I guess it's not on the gravel and definitely not around the filter flow. The gravel is covered in the brown algae.

Maybe rather than introduce an algae eater I will increase the frequency of my water changes and do 50% instead of 25%. The green algae (likely cyano I guess) first appeared when I still had the ADF tadpole in a breeder net. Could small bits of algae tabs I crushed up for the tadpole be the cause? Once the tad became a froglet, I switched over to frozen brine shrimp, but maybe the algae had taken hold by then?

I hesitate to add live plants because I'm not sure I can handle it. A friend of mine had live plants in his tank and the water was always incredibly green and cloudy. I'm glad to know it sounds like this algae is a normal reaction due to the lack of live plants. It's just a little unsightly. Do you think I'll be able to get rid of it just by adjusting my water changes? And continuing to brush it off the decor?

I'm having more algae than normal lately (which is weird since it's winter and there is less daylight and the lighting of the room/tank haven't changed). Thanks!

Steph

I have also noticed an increase in algae lately and think one contributing factor is the season. The sun is low in the sky this time of year and the trees have lost their leaves so my tank is now actually getting more direct sun light than it did in summer. Could this be your situation too?

The tank has been up and running for almost two years now. Would that mean that the brown algae isn't diatoms? It could be a low light thing. I don't know what silicates are though and why I would have them in my tank.

If the brown comes off easily with your fingers, sort of disintengrating, it is diatoms. Usually in low light, and/or silicates which are a type of mineral that can be present in tap water. Silica sand is from silicate mineral, and some suggest this can cause diatoms but others say no. More likely in your tap water, you can check the water supply folks for the water data and see if it lists silicates.

The brown could be a type of brush algae, if it does not easily come off on your fingers. This is the more likely, given a tank with no plants and light.

There are several pictures of this person's tank and in a couple you can see the green feathery algae on the white plants. That looks like what I have. So it's cyano? But this is not a problem right, just unsightly? I guess it's not on the gravel and definitely not around the filter flow.

The green on the white feather plants in those photos 5 & 6, as I mentioned in that thread, it is cyanobacteria. It is a green slime, it will easily come off on your fingers and feels slimy and can stain your fingers green. This is not healthy and should be dealt with as I set out in that thread. Caused by high organics, so more frequent water changes (or more volume), good vacuuming of the substrate, not overfeeding or over stocking, etc.

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The gravel is covered in the brown algae.

Try the finger test mentioned above to determine what this may be.

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Maybe rather than introduce an algae eater I will increase the frequency of my water changes and do 50% instead of 25%. The green algae (likely cyano I guess) first appeared when I still had the ADF tadpole in a breeder net. Could small bits of algae tabs I crushed up for the tadpole be the cause? Once the tad became a froglet, I switched over to frozen brine shrimp, but maybe the algae had taken hold by then?

Organics will occur from any dead animal, fish or plant matter, including fish foods. And these cause cyanobacteria, with light present.

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I hesitate to add live plants because I'm not sure I can handle it. A friend of mine had live plants in his tank and the water was always incredibly green and cloudy. I'm glad to know it sounds like this algae is a normal reaction due to the lack of live plants. It's just a little unsightly. Do you think I'll be able to get rid of it just by adjusting my water changes? And continuing to brush it off the decor?

The cyano I would deal with. The other algae, it is up to you. But live plants are such a benefit to fish that there really is no reason not to have some. They filter the water better than any filter we can think up. Plus they give shade to fish. And reduce fish stress, and on this pint I will expand.

Cardinal tetra have very specific biotopes. They are only found in streams that either have aquatic vegetation (plants), or overhanging marginal vegetation. Cardinals never, absolutely never, venture into open water except to escape a predator. They have what Baensch calls a light phobia; lack of branches and/or plants makes them stressed, and shortens their lifespan.

I have maintained groups of this beautiful fish for many years. In every tank, they always remain within plants, under leaves, etc. They are even reluctant to approach the surface for food, though they usually do, but they clearly prefer remaining down in the shade and getting food particles that float down. Many species of characins behave similarly; most of the Rosy clade in Hyphessobrycon for example (Rosy Tetra, Roberts Tetra, Black Phantom Tetra, etc). It is one thing to research a species and read this, but when you have the opportunity of having them in a 5 or 6 foot tank where you can provide shade in places and open areas elsewhere and then observe them remaining within the planted shady areas without fail, you begin to understand why this is important.

Fish have evolved over thousands of years for their particular habitat, and providing an aquascape as close as we can to what they "need" in a very real sense will always result in healthier fish. I was reading an article the other day on one of the fish periodicals, forgotten the author now, but he made a profound comment. What on earth makes us so foolish as to think that millions of years of natural selection and evolution can be somehow changed in a few generations of tank-raised fish? The answer of course is that it can't.

Anyway, back to live plants; these are no more difficult that keeping fish healthy. Plants like fish need some basics, and if these are provided, they will prosper. We can discuss further if you like; have a read of my 4-part article stickied at the top of the Aquarium Plants section for a simple approach. And check the photos of my tanks that follow this approach; click "Aquariums" below my name on the left.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

Thanks so much for all your help Byron. I have been looking up common freshwater aquarium algae and I think the brown is definitely diatoms. It brushes away very easily. I guess I have it because of low light conditions.

The greenish algae might be cyanobacteria, but after looking at other photos of other algae, I'm wondering if it might rather be a type of brush algae? Tough to tell and I can't seem to get a good photo. If it is a green brush algae I think I saw the recommendation was to cut some of the light. But if I need more light to get rid of the diatoms...? I'm confused.

Today before I did a water change I checked the ammonia, nitrite, and nitrate levels. The ammonia and nitrite were both 0 as usual. However the nitrates, which have always held steady in my tank between 20-40ppm, registered 0 today. That seems weird. Could that be related to my algae issue?

I did a 75% water change today and really scraped the sides of the tank well and scrubbed off all the decor. I vacuumed my gravel as usual. All the cleaning kicked up a bunch of the green algae and the water in my bucket was filled with the tiny floaty green bits. I also changed my carbon filter.

I will stick with the frequent heavy water changes, but what do you think regarding light? The tank doesn't really get any direct sunlight, the windows in the room are sort of north-east facing. I have the tank light on about 6-7 hours a day usually. Also, the nitrates level is odd to me. Most of what I read talks about the dangers of high nitrates, but I haven't found anything about low or no nitrates. Any thoughts?

Oh, and thanks for the recommendation. I will read up some on adding plants to the tank.